Izzet Delver is a fast aggro-control deck leaning on Dragon's Rage Channeler and Murktide Regent protected by Force of Will and Daze, so Dismember is cheap removal that cleanly answers Dragon's Rage Channeler and can handle a Murktide Regent that comes down small. Disruptor Flute naming Force of Will or Daze taxes that card by {3} even when it is cast for its alternative cost, buying time for Urza's Saga and Ancient Tomb to assemble our engine. Defense Grid stays in because it makes every spell they cast on our turn cost {3} more, including Force of Will and Daze cast for their alternative costs, so those counters are no longer free; we mostly act on our own turn, where our spells are not taxed. Pithing Needle, Expedition Map, and Karakas aren't high-impact against their nonlegendary creature-based plan, and Mystic Forge is a slow four-mana artifact that does little against a fast tempo deck. Keep our flexible Kozilek's Command mode available to exile Dragon's Rage Channeler before it hits delirium.